The present invention relates to a retainer assembly for at least one fastener, for example a nut or a bolt, in which the fastener is floatingly retained within a channel member, and to a clamping system which includes complementary fastener retainer assemblies.
Floating nut and bolt retainers in which a nut or bolt is retained or "captivated" with one or more directions of limited movement in a channel member are known in the art.
Retainers in which the nut or bolt is self-wrenching and retained with limited movement are particularly useful in "blind fastening" operations and have been used extensively in aircraft construction. Such retainers are also quite useful in operations where, though both complementary fastener parts are accessible, it is inconvenient or impractical for a worker to use both hands to engage the complementary fasteners. This may be caused by poor accessibility or a difficulty in being able to use both hands to work both complementary fasteners, as for example where the structure being fastened must be manipulated or held in position.
One reason for allowing limited movement of a retained nut for example is to facilitate alignment of the nut with the bolt being threaded to it so as to reduce substantially the frequency of cross-threading. Also, allowing a limited movement of the nut substantially reduces galling and coldwelded seizures of the bolt to the nut.
A typical nut retainer assembly, or simply a nut retainer, is disclosed in U.S. Pat. No. 2,144,350 issued Jan. 17, 1939. The channel member of that retainer includes a web portion and spaced flange portions extending at right angles from the same side of the web portion. The edge of each flange portion is inturned towards the opposite flange portion. The resulting structure defines generally a C-shaped channel member. One or more holes are provided in the web portion and one or more corresponding nuts are disposed in the channel member, each with its bore generally registered with a respective hole in the web portion. In order to retain a nut once it has been inserted into the channel member, the distance between the inturned flange edges is less than the distance between flats of the nut; the width of the web portion is only slightly greater than the distance between flats of the nut; and the height of the flange portions, i.e., the distance from the web portion to the inturned flange edges, is slightly greater than the height of the nut. The inturned flange edges should overlap the nut by a sufficient distance to provide a desired level of resistance to "push-out" force, i.e., force applied to the nut tending to push it out of captivation through the opening between the inturned flange edges. The nuts are inserted into the channel member through an end thereof. In the apparatus of U.S. Pat. No. 2,144,350, once a nut is positioned in the channel member over a hole in the web portion its longitudinal movement is limited by bending or crimping the inturned flange edges adjacent the nut. Lances or tabs in the web portion, the flange portions or the inturned flange edges can also be used to limit longitudinal movement of the nut.
In a nut retainer of the kind described in U.S. Pat. No. 2,144,350, the movement of the nut relative to the channel member is limited in three directions, i.e., in the direction of the longitudinal extent of the web portion by the crimping, in the direction of the width of the web portion by the relative dimensions of the web portion and the nut, and in the direction of the height of the flange portions by the relative heights of the flange portions and the nut. In addition, the thickness of the flange portions is selected to resist excessive flexing so as to permit only limited rotation between the nut and the web portion, thereby providing for self-wrenching of the nut.
However, in a nut retainer of the kind described, it is not possible to insert the nut into or remove the nut from the channel member through the space between the inturned flange edges without permanent or plastic deformation of the channel member, the use of special tools or the application of very high forces. Thus, as indicated above, the nut is inserted from an end of the channel member and also removed in the same manner, noting that removal, if at all possible, is hindered by the presence of the crimping and other captivated nuts.
Cross-threading and galling leading to seizure of a nut and bolt renders them unusable. When a seizure occurs, the bolt must be separated from the nut by cutting or shearing it, for example by applying additional torque to the bolt, thereby leaving the nut with a part of the bolt threaded to it. When it is necessary to replace a nut in nut retainers of the type described above, the entire retainer assembly has to be replaced since a captivated nut cannot easily be removed and replaced, and that replacement is costly and time consuming.
There is therefore a need for a retainer having floating fasteners in which a captivated fastener can be replaced without replacing the entire retainer assembly.
It is known, however, to removably insert a nut into a C-shaped channel member through the opening between the inturned flange edges using a snapped-in cap member (U.S. Pat. No. 2,575,594 issued Nov. 20, 1951) or a housing having a tab which snaps into engagement with one of the flange edges (U.S. Pat. No. 2,438,044 issued Mar. 16, 1948). However, the additional structure in the form of a cap or housing adds to the material cost and labor cost for manufacturing and assembling the retainer. Additionally, due to the need for "snap action", the cap or housing is typically fabricated of sheet material and may not possess a high resistance to "push-out" force.
Another nut retainer in which the nut can be inserted through the opening between inturned flange edges of a C-shaped channel member is disclosed in U.S. Pat. No. 3,493,025 issued Feb. 3, 1970. The nut and the inturned flange edges include cooperating structure for supporting the nut from the inturned flange edges spaced from the web portion of the channel member. The nut is inserted through the opening between the inturned flange edges and indexed by 90.degree. to engage the structure for supporting the nut. The nut receives a bolt through the opening between the inturned flange edges rather than through an opening in the web portion. As a result, the web portion is not used as a pressure distributing surface. The cooperating supporting structure of the nut and inturned flange edges frictionally engages the nut so as to inhibit movement of the nut. Thus, the nut is not floating. Also, the additional cooperating structure for supporting the nut adds to the material and labor cost for manufacturing and assembling the nut retainer.
Thus, while it may be possible to remove an unusable nut from the nut retainers of the three patents described above through the opening between the inturned flange edges, those nut retainers suffer from the deficiencies indicated.